1882.] 275 [Chase. 



we hear, and Anderssohn* has experimentally shown that they can ade- 

 quately represent all varieties of gravitating and electromagnetic phe- 

 nomena. 



225. A Scientific Statement of the Tidal Problems. 



The "Astronomy for Schools and Colleges," by Newcomb and Holden 

 (Ed. of 1879, p. 1G7), speaks with true scientific caution, as follows: — 

 "The theory of the tides offers very complicated problems, which have 

 taxed the powers of mathematicians for several generations. These prob- 

 lems are in their elements less simple than those presented by the motions 

 of the planets, owing to the number of disturbing circumstances which 

 enter into them. The various depths of the ocean at different points, the 

 friction of the water, its momentum when it is once in motion, the effect 

 of the coast-lines, have all to be taken into account. These quantities are 

 so far from being exactly known that the theory of the tides can be ex- 

 pressed only by some general principles which do not suffice to enable us 

 to predict them for any given place. ' ' 



236. Cometary Spectra. 



The uncertainties of measurement antl the harmonic indications which 

 are given in spite of those uncertainties may be illustrated by comparing 

 observations of like objects by different reporters. Tacchini gives {Ann. 

 de Chim. et de Phys., xxv, SS6) measurements of the spectral lines in comet 

 b, 1881, which correspond satisfactorily with lines in Hesselber's carbon 

 spectrum. The harmonic accordance is equally satisfactory. 



Harmonic. Tacchini. 



37527.7 -H 68 == 551.9 552.1 



37527.7 -^ 78 = 514.1 514.1 



37527. 7 H- 81 = 463. 2 463. 1 



Thollon {lb., 287-8) compares the same spectrum with three different 

 spectra of carbon compounds, viz : A, electric arc, Jamin'slamp measure- 

 ments made by M. Bigourdan ; B, cyanogen, coil and condenser, Salet ; 

 C, blue flame of illuminating gas, Lecoq de Boisbaudran. 



Harmonic. Thollon. A. B. C. 



31479 --56 = 562.1 562 562.2 563.0 562.9 



31479 -- 61 = 516.0 516 516.5 516.3 516.1 



31479 -- 67 = 469.9 470 470.4 470.0 470. 6 f 



*• The harmonic divisors for Tacchini's measurements are sums of succes- 

 sive or nearly successive phyllotactic numbers : 81 = 5 -f 8 -f 13 -f 21 

 + 34; 73 = 81 — 8;. 68=73 — 5:^13 + 21-1-34. In the harmonic divisors 

 for Thollon's measurements, 56 =: 7 x 8 = product of the artiad and 

 perissad divisors, and the middle line is an arithmetical mean between the 

 other two. 



* Der Mechanik der Gravitation. Breslau, 1874 ; J. B. des Bres. Phys. Ver.. 1881-2. 

 t Boishaudran does not give this line, but he gives 473.8 and 467.5, the arith- 

 metical mean being 470.65. 



PROC. AMER. PHILOS. SOc! XX. 111. 2l. PRINTED .JUNE 3, 1882. 



